The present invention relates to a magnetic recording medium used in an apparatus such as a magnetic disk apparatus; to a process for producing the magnetic recording medium; to a magnetic recording and reproducing apparatus including the magnetic recording medium; and to a medium substrate used in the magnetic recording medium.
Hitherto, typical magnetic recording media have a structure including a substrate formed from a metal such as aluminum, an NiP-based-alloy film formed on the substrate, and a non-magnetic undercoat film and a magnetic film formed on the NiP-based alloy film, where the alloy film is textured to impart anisotropy to the magnetic film.
In recent years, as substrates for producing magnetic recording media, non-metallic substrates formed from a material such as glass have substituted for metallic substrates. Non-metallic substrates have an advantage in that they do not easily permit head slap to occur, because of their high hardness. In addition, from the viewpoint of glide height characteristics, non-metallic substrates are advantageous, because of their high surface evenness. However, non-metallic substrates are difficult to texture. Therefore, it has been proposed that an NiP-based-alloy film be formed on the surface of a non-metallic substrate, and that the surface of the alloy film be subjected to texturing.
An NiP-based-alloy film is formed through electroless plating or sputtering.
Although an NiP-based-alloy film formed through electroless plating has high hardness and exhibits excellent durability, the film also has a problem in that the production process for the film is intricate. Therefore, in order to produce an NiP-based-alloy film, sputtering is typically employed in view of its excellent production efficiency.
However, since an NiP-based-alloy film formed through sputtering has a hardness lower than that of an NiP-based-alloy film formed through electroless plating, when the sputtered film is subjected to texturing, burrs are easily formed on its surface, and abrasive grains are easily left on the surface. Particularly, when the thickness of the sputtered film is large, the surface configuration of the film tends to become non-uniform, potentially resulting in unsatisfactory glide height characteristics.
In order to enhance glide height characteristics effectively, the thickness of an NiP-based-alloy film is reduced, thereby causing the surface configuration of the film to become uniform.
However, when an NiP-based-alloy film is formed to be thin, application of bias to the film becomes difficult during formation of a non-magnetic undercoat film and a magnetic film, and thus the crystal structure of the films formed is impaired. As a result, the crystal orientation of the non-magnetic undercoat film and the magnetic film is impaired, potentially causing deterioration of magnetic characteristics such as noise characteristics.
It has been considered that, even when an NiP-based-alloy film is thin, if a thick metallic film formed from, for example, Cr is provided between the alloy film and a substrate, bias can be easily applied to the alloy film during formation of a non-magnetic undercoat film and a magnetic film.
However, in this case, since crystal growth of the thick metallic film proceeds excessively, the non-magnetic undercoat film which is formed on the thin NiP-based-alloy film, which is formed on the metallic film, is affected strongly by the crystallinity of the metallic film. Therefore, the crystal orientation of the non-magnetic undercoat film is impaired, potentially causing deterioration of magnetic characteristics such as noise characteristics.
In order to subject an NiP-based-alloy film to effective texturing, the NiP-based-alloy film can be formed from an alloy of NiP containing an element such as Mo, to increase the hardness of the film.
When an NiP-based-alloy film is formed from the aforementioned alloy, even if the thickness of the alloy film is increased in consideration of bias application during formation of a non-magnetic undercoat film and a magnetic film, goodxe2x80x94to some extentxe2x80x94texturing-related properties can be ensured. However, even in this case, it is currently difficult to obtain satisfactory glide height characteristics to attain high recording density.
In view of the foregoing, an object of the present invention is to provide a magnetic recording medium which exhibits excellent glide height characteristics and excellent magnetic characteristics such as noise characteristics.
Another object of the present invention is to provide a process for producing the medium.
Still another object of the present invention is to provide a magnetic recording and reproducing apparatus.
A further object of the present invention is to provide a substrate used in the medium.
The present invention provides a magnetic recording medium comprising, in order, a non-metallic substrate an amorphous metallic film having an amorphous structure, a crystal-structure-regulating film, a non-magnetic undercoat film and a magnetic film, and wherein the thickness of the crystal-structure-regulating film is 50 nm or less, and the total thickness of the amorphous metallic film and the crystal-structure-regulating film is at least 60 nm.
Preferably, the amorphous metallic film is formed from one or more elements selected from among Cr, Co, Ta, Nb, Si, Al, Ti, Zr, W, and Mo.
Preferably, the amorphous metallic film is formed from a CrTa-based alloy or a CrSi-based alloy.
The crystal-structure-regulating film preferably has an average surface roughness (Ra) of 0.5 nm or less, more preferably 0.05-0.5 nm.
Preferably, the P content of the NiP-based alloy constituting the crystal-structure-regulating film is 15-25 at %.
The present invention also provides a process for producing a magnetic recording medium, which comprises forming, on a non-metallic substrate, an amorphous metallic film, a crystal-structure-regulating film, a non-magnetic undercoat film, and a magnetic film, in order, and wherein the thickness of the crystal-structure-regulating film is 50 nm or less, and the total thickness of the amorphous metallic film and the crystal-structure-regulating film is at least 60 nm.
The present invention also provides a magnetic recording and reproducing apparatus comprising a magnetic recording medium and a magnetic head for recording data onto the medium and reproducing the data therefrom, wherein the magnetic recording medium comprises a non-metallic substrate; a crystal-structure-regulating film of NiP-based alloy formed thereon; and a non-magnetic undercoat film and a magnetic film formed on the crystal-structure-regulating film; with an amorphous metallic film having an amorphous structure provided between the non-metallic substrate and the crystal-structure-regulating film, and wherein the thickness of the crystal-structure-regulating film is 50 nm or less, and the total thickness of the amorphous metallic film and the crystal-structure-regulating film is at least 60 nm.
The present invention further provides a medium substrate comprising a non-metallic substrate; an amorphous metallic film having an amorphous structure provided thereon; and a crystal-structure-regulating film of NiP-based alloy formed on the amorphous metallic film, and wherein the thickness of the crystal-structure-regulating film is 50 nm or less, and the total thickness of the amorphous metallic film and the crystal-structure-regulating film is at least 60 nm.